It is common practice for fuel cell vehicles that gaseous hydrogen stored at high pressure in a storage tank at a gas station or the like is filled into their vehicular tanks. At present, the pressure of gaseous hydrogen stored in the storage tank is standardized to be 25 MPa or 35 MPa.
A pipe coupling that handles such a high-pressure fluid is arranged as follows. A female coupling member receives a tubular forward end portion of a male coupling member into a tubular forward end portion thereof. In this state, a coupling locking mechanism is acted upon from the outside of the tubular forward end portion of the male coupling member to lock the male coupling member to the female coupling member in coupled relation. In addition, an axially displaceable tubular valving element is provided in the tubular forward end portion of the female coupling member. When the male coupling member and the female coupling member are coupled and locked in coupled relation, the valving element is inserted into a valving element receiving part formed at a forward end portion of a through-hole longitudinally extending through the male coupling member. Thus, the valving element hermetically engages an O-ring attached to the through-hole wall surface that defines the valving element receiving part, and the valving element is displaced backward, whereby the through-hole (fluid passage) of the pipe coupling is opened. That is, the fluid is allowed to flow between the male coupling member and the female coupling member through the tubular valving element. Pipe couplings arranged as stated above are disclosed, for example, in Japanese Patent Number 2694302, Japanese Patent Application Publication No. 2003-97782 and Published Japanese Translation of PCT International Publication for Patent Application No. 2000-515953.
When a high-pressure fluid is to be supplied from a storage tank to a vehicular tank, a female coupling member connected to the storage tank is coupled to a male coupling member connected to the vehicular tank. Regarding male coupling members, it is specified that those manufactured according to 25 MPa pressure specifications shall be able to couple only to female coupling members manufactured according to 25 MPa pressure specifications and unable to couple to female coupling members according to 35 MPa pressure specifications, and that male coupling members according to 35 MPa pressure specifications shall be able to couple not only to female coupling members according to 35 MPa pressure specifications but also to those according to 25 MPa pressure specifications.
To achieve differentiation in coupling between male and female coupling members as stated above, according to one method, the forward end portions of female coupling members manufactured according to the 35 MPa pressure specifications are made longer than those of female coupling members according to the 25 MPa pressure specifications. Meanwhile, male coupling members manufactured according to the 35 MPa pressure specifications have a tubular forward end portion with a length that allows it to be inserted as far as the coupling locking position in the tubular forward end portion of a female coupling member regardless of whether it complies with the 25 MPa or 35 MPa pressure specifications. Male coupling members manufactured according to the 25 MPa pressure specifications have a tubular forward end portion with a length that allows it to be inserted as far as the coupling locking position in the tubular forward end portion of only a female coupling member according to the 25 MPa pressure specifications.
In this case, both female coupling members complying with the 25 MPa and 35 MPa pressure specifications have tubular valving elements of the same diameter for male coupling members. When a male coupling member is inserted into and coupled to either of the female coupling members, the valving element is inserted into a valving element receiving part provided in the male coupling member and hermetically engaged with an O-ring fitted to the wall surface of the valving element receiving part.
Recently, standardization of higher fluid pressures such as 50 MPa and 70 MPa has been under discussion. When handling a fluid under a pressure of 50 MPa or 70 MPa, differentiation in coupling between female and male coupling members can be achieved in the same way as the above. The tubular valving element for passing a fluid, however, needs to ensure the pressure resistance required therefor by reducing the diameter of the fluid passage extending therethrough. Consequently, the outer diameter of the tubular valving element also becomes small as compared with those handling a fluid pressure of 25 MPa or 35 MPa. Accordingly, the male coupling member requires a valving element receiving part for receiving the valving element with a reduced diameter and hence needs an O-ring that is provided in this valving element receiving part to hermetically engage the valving element.
When a male coupling member having valving element receiving parts with different diameters as stated above is coupled to a female coupling member according to the 25 MPa or 35 MPa pressure specifications, the valving element of the female coupling member is not inserted into the valving element receiving part for a female coupling member according to the 50 MPa or 70 MPa pressure specifications. Consequently, the O-ring for the valving element of a female coupling member according to the 50 MPa or 70 MPa pressure specifications is subjected to a fluid pressure of 25 MPa or 35 MPa and hence likely to detach from the wall surface of the valving element receiving part. Therefore, when the male coupling member is coupled to a female coupling member according to the 50 MPa or 70 MPa pressure specifications, the valving element may fail to be hermetically engaged with the O-ring, which is dangerous.